1. Field of the Invention
This invention relates to a surface mounting type electronic circuit unit.
2. Description of the Related Art
In general, a surface mounting type electronic circuit unit of this type has a structure in which various circuit parts are soldered on soldering lands of a conducting pattern formed on a substrate and these circuit parts are covered with a shield cover. The substrate has side end electrodes on the side thereof, and the side end electrodes are soldered on soldering lands of a mother substrate when the electronic circuit unit is surface-mounted on the mother substrate. The circuit parts are used depending on the required circuit structure such as a tuning circuit, resonance circuit, or amplifier circuit. For example, the transistor, chip resistance, chip capacitor, and inductor are used as the circuit parts of an amplifier circuit, and these circuit parts are connected through the conducting pattern.
Recently, the technique for miniaturizing the circuit parts such as chip parts and transistor has been progressed markedly, and for example, the ultra-small chip resistor and chip capacitor having an apparent size of approximately 0.6xc3x970.3 mm have been used practically. Therefore, it is possible that such small-size chip parts and transistor are used for the above-mentioned convention electronic circuit unit and are mounted on a substrate with narrow pitch between circuit parts to thereby miniaturize the electronic circuit unit to a certain extent. However, the miniaturization of the circuit parts such as chip parts and transistor is limited, and narrowing of the pitch between parts is limited because many circuit parts should be mounted on a substrate so that soldered portions of individual circuit parts are prevented from short-circuiting. These limitations have prevented further miniaturization of the electronic circuit unit.
Furthermore, in the case where an electronic circuit unit of this type has, for example, an amplifier circuit, general-use chip resistors having a resistance value that has been trimmed previously to a desired value have been used as all resistors that are necessary for the amplifier circuit in the above-mentioned conventional art. However, if the mounted chip resistors have some resistance value dispersion, then the collector current of the transistor is dispersed, and the troublesome output adjustment is required.
The present invention has been accomplished in view of the problem of the conventional art, and it is the object of the present invention to provide an electronic circuit unit that is suitable for miniaturization and is suitable for simple output adjustment.
To achieve the above-mentioned object, an electronic circuit unit of the present invention comprises circuit elements including capacitors, resistors, and inductance elements formed on an alumina substrate by means of thin film forming technique, and a semiconductor bare chip of a transistor fixed to the alumina substrate by means of wire bonding, wherein the transistor has at least a first transistor, and only the emitter resistor, out of a base bias voltage dividing resistor and an emitter resistor of the first transistor, is trimmed to set the current value of the first transistor.
According to the above-mentioned structure, because circuit elements including capacitors, resistors, and inductance elements are formed with high precision by means of thin film forming technique and a semiconductor bare chip of a transistor is fixed by means of wire bonding, necessary circuit parts are mounted in high density on an alumina substrate and a surface mounting type electronic circuit unit that is suitable for miniaturization is realized. Furthermore, even if individual base bias voltage dividing resistors formed on an alumina substrate by means of thin film forming technique have some resistance value dispersion, because the collector current value can be varied by trimming only the emitter resistor, the resistance value can be trimmed at one location for output adjustment.
Furthermore, in the case where the transistor has first transistor and second transistor connected in series, it is preferable that only the emitter resistor of the first transistor, out of the base bias voltage dividing resistors and emitter resistors of the first and second transistors, is trimmed to set the current value of both transistors. Trimming of all the base bias voltage dividing resistors can be omitted and only the emitter resistor of the first transistor may be trimmed.
Furthermore, the electronic circuit unit of the present invention has circuit elements including capacitors, resistors, and inductance elements formed on an alumina substrate by means of thin film forming technique, and a semiconductor bare chip of a transistor fixed to the alumina substrate by wire bonding, wherein the transistor has at least a first transistor, and base bias voltage dividing resistors used for applying a voltage on the base of the first transistor are formed proximate to each other on the alumina substrate by means of thin film forming technique.
According to the above-mentioned structure, because circuit elements including capacitors, resistors, and inductance elements are formed with high precision by means of thin film forming technique and a semiconductor bare chip of a transistor is fixed by means of wire bonding, necessary circuit parts are mounted in high density on an alumina substrate and a surface mounting type electronic circuit unit that is suitable for miniaturization is realized. Furthermore, though the absolute value of resistors formed on the alumina substrate by means of thin film forming technique has some dispersion, because a plurality of base bias voltage dividing resistors used to apply a voltage on the transistor are formed proximate to each other by means of thin film forming technique, the ratio of dispersion of the resistors is almost equalized, and trimming of the resistor value can be omitted.
Furthermore, in the case where the transistor has a first transistor and second transistor connected each other in series, it is preferable that base bias voltage dividing resistors of the first and second transistors are formed proximate to each other on the alumina substrate by means of thin film forming technique. Thereby, trimming of all the base bias voltage dividing resistors can be omitted.
Furthermore, in the case of the above-mentioned structure, it is preferable that a part of or all of the plurality of base bias voltage dividing resistances are located on a plurality of lines. Thereby, the base bias voltage dividing resistors are disposed efficiently on a limited space of the alumina substrate.